The general objective of this proposal is to define the role of tyrosine residue phosphorylation in the regulation of protein kinase C delta (PKCd) in myocardial tissue. The hypothesis to be tested is that agonist-specific activation of PKCd involves tyrosine phosphorylation which modifies PKC myofilament substrate specificity and kinase activity. Experiments will characterize tyrosine phosphorylation status on PKCd with various stimuli and the impact on myocyte mechanical function. In addition, the effect of tyrosine residue replacement with unphosphorylatable or pseudo-phosphorylated amino acids in the hinge, pseudosubstrate, and activation loop domains on PKCd localization and substrate specificity will be determined. Finally, experiments will resolve whether PKCd activation promotes the activity of other signal transduction pathways involved in regulation pathophysiological processes (hypertrophy or apoptosis. Compelling preliminary evidence indicates phosphorylation of specific tyrosine residues of PKCd alters substrate specificity particularly in respect to troponin (Tn) complex components. In addition, phosphorylated tyrosine (pY) may change the cofactor requirements of the kinase enabling lipid independent activity. Results will provide novel information regarding stimuli specific PKCd activation and activity as well as the effect on cardiac myofilament phosphorylation and myocyte functional capabilities. [unreadable] [unreadable] [unreadable]